1. Field of the Invention
The present invention relates to a multiplexed audio data decoding apparatus for decoding voice/audio signals which are encoded with compression format, and in particular, to a multiplexed audio data decoding apparatus and a receiver apparatus which can be used preferably as a receiver for digitized broadcasting, in which many channels are multiplexed.
2. Description of Prior Art
As a method being applied to, in general, for compressing digital audio signals, there are known MPEG (Moving Picture Experts Group) Audio and a method so-called by xe2x80x9cAC-3xe2x80x9d which is applied to by ATSC (United States Advanced Television System Committee). Both of those methods are based upon a technology, in which information on a time axis is converted into data on a frequency axis, and is compressed by dividing it into frequency bands with using a psychological auditory characteristic, such as masking effects, or by using correlation between audio channels.
A method for decoding audio bit streams which are compressed by using those methods, being based on DSP (Digital Signal Processor), is described in xe2x80x9cDesign And Implementation of AC-3 Codes, Vol. 41, No. 3, August 1995xe2x80x9d, as an audio decoder corresponding to the AC-3 format. The DSP, in the same manner as a general micro-controller, takes a method of processing data by interpreting the software program codes in a built-in register(s) so as to store them into a memory(s). Therefore, as compared to the method for realizing or achieving it by means of hardware, it is possible for it to have decoding algorithms in plural formats as decoding process codes for each, and also it has a flexibility with the changes thereof, thereby being considered to be advantageous in both view points of costs and handling property thereof. Further, it is characterized by the fact that the calculation speed thereof is improved, by devising or providing a means of hardware for exclusive use, such as a high speed multiplier, or by smoothing the data flow therein with provision of a plurality number of data buses.
In an audio decoder based upon the DSP, in general, steps for the decoding processes are memorized in the built-in ROM as the program codes. This is due to the fact the ROM must be connected to the DSP, directly, because the program codes are exclusive only for use of readout thereof, and for the purpose of avoiding the losses thereof during access cycles (1 command/1 cycle in an ordinary DSP).
In a case of viewing the audio decoder as a part of a digital broadcast receiver, various conditions are required for compression rate and sound quality depending upon communication situations or conditions at a supply side, including contents of services, a broadcasting satellite, a communication satellite, ground wave, and wired cable, etc., for examples, and a format must be selected most appropriately for respective one of them. Therefore there is a necessity for a receiver side to corresponds to those plural formats.
Here, for corresponding to the plural kinds of the compression code formats by means of one DSP chip, there is a necessity that the program codes for each of the formats are maintained in a form of the built-in ROM. And, not only for the program codes, but also for each of the formats, a table for the exclusive use for invariables or constants is necessary in the form of the built-in ROM. Accordingly, from a view point of scale in circuitry, there is a problem that it is difficult to integrate the audio decoder including the DSP. Also, in a case where the number of the formats to be processed increases or when trying to change the specification, since the built-in ROM cannot be easily changed therein, there is also a problem that the flexibility is decreased down.
An object of the present invention is to provide a multiplexed audio data decoder apparatus and a receiver apparatus, in which integration of the audio decoder is easy, therefore, having a high flexibility even in the case where the number of the formats to be processed increases or when trying to change the specification.
(1) For achieving the object mentioned above, according to the present invention, there is provided a multiplexed audio data decoder apparatus, for inputting a group of packets, each being formed by packetizing audio data sequences which are compressed and encoded and by multiplexing a plurality of those sequences, and for selectively decoding one audio data sequence which is designated by a user, comprising: a demultiplexer for extracting the one audio data sequence which is designated by the user from said group of packets depending upon a property or attribute information which each packet has, and further for extracting a method of the compression and encoding which is applied for compressing the audio data sequence from a header information which said each audio data sequence has; a first memory in which decoding process codes corresponding to said method of the compression and encoding; a digital signal processor for decoding the compressed audio data sequences in accordance with said decoding process codes, sequentially; a read-only memory, in which are accumulated a plurality of the decoding process codes, each corresponding to each one of said plural methods of the compression and encoding; and controller means for detecting change in said method of the compression and encoding, and for transferring the decoding process code corresponding to the method of the compression and encoding after being changed, from said read-only memory to said first memory, wherein said digital signal processor begins decoded process by using the decoding process code which is transferred to said first memory.
With such the construction, since the plural kinds of decoding process codes are stored in the read-only memory, it is possible to correspond or deal with the increase in the number of the formats to be processed and/or the change in the specification, by interchange of the read-only memory, with ease, as well as to improve flexibility thereof.
(2) For achieving the object mentioned above, according to the present invention, there is provided a multiplexed audio data decoder apparatus, for inputting a group of packets, each being formed by packetizing audio data sequences which are compressed and encoded and by multiplexing a plurality of those sequences, and for selectively decoding one set of a video data sequence and an audio data sequence accompanying therewith, which is designated by a user, comprising: a demultiplexer for extracting the one audio data sequence which is designated by the user from said group of packets depending upon a property or attribute information which each packet has, and further for extracting a method of the compression and encoding which is applied for compressing the audio data sequence from a header information which said each audio data sequence has; a first memory in which decoding process codes corresponding to said method of the compression and encoding; a digital signal processor for decoding the compressed audio data sequences in accordance with said decoding process codes, sequentially; a read-only memory, in which are accumulated a plurality of the decoding process codes, each corresponding to each one of said plural methods of the compression and encoding; a video decoder for decoding said video data sequence which is compressed and encoded; a second memory which said digital signal processor and said video decoder use as work area for the decoding process thereof; and controller means for transferring said plural decoding process codes from said read-only memory to said second memory in advance, as well as for detecting change in said method of the compression and encoding, and for transferring the decoding process code corresponding to the method of the compression and encoding after being changed, from said read-only memory to said first memory, wherein said digital signal processor begins decoding process by using the decoding process code which is transferred to said first memory.
With such the construction, since the plural kinds of decoding process codes are stored in the read-only memory, it is possible to correspond or deal with the increase in the number of the formats to be processed and/or the change in the specification, by interchange of the read-only memory, with ease, as well as to improve flexibility thereof.
(3) In the above-mentioned (1) or (2), preferably, after transmitting the decoding process code corresponding to the compressing and decoding method after the change thereof, from said read-only memory to said first or second memory, the digital signal processor conducts the process for deciding the presence of the transmission error.
(4) In the above-mentioned (3), preferably, in the decision process for deciding the presence of the transmission error, which is conducted by said digital signal processor, the audio data sequence specific to the decoding process code is decoded, so as to be compared with an expected value corresponding thereto.